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03 - Bash variables


The bash scripts allow for the use of variables. The variable declaration is:

variable_name = value

The scope of this variable is the script where it was created in. To make it available to other programs or scripts, you can write:

export variable_name

To print on the screen the value of a variable you can write (remember to put the dollar sign):

echo $variable_name

To assign the value of a variable to another variable, you can write:


Quotes usage
In the bash there are three strings delimiters: the grave accent, the single quotes and the double quotes. Each one gives a different behaviour:
  1. Double quotes: (that is "): visualize a string substituting it with its value.
  2. Single quotes (that is '): don't substitute the value of a variable to its name.
  3. Grave accents (that is `): substitute to the string the result of its execution (useful for example when you want to save the output of a command in a variable).
Let's see an example


echo "   The variable is: $x" #Prints "   The variable is: 5"
echo '   The variable is: $x' #Prints "   The variable is: $x"

Arithmetical operations
To execute arithmetical operations you can use two different syntaxes:
  1. expr included between grave accents (be careful not to use the apostrophe!).
  2. double parenthesis with the dollar sign.
This is an example:


x=`expr $x + 1`

echo $x

The allowed mathematical operations are:

%Module or remainder


Fatal error: Call to undefined function sqlite_open() in /membri/giacobbe85/include/ on line 324